# UA Restrictions

Zenlayer CDN allows you to configure a User-Agent blacklist identify and filter requests. This way, you can restrict access to CDN resources and improve service security.

User-Agent is an HTTP header. It contains the information about the client that makes the request, including the operating system (OS), OS version, browser, and browser version.

User-Agent blacklist: Requests whose User-Agent header has a value in the blacklist are rejected. The HTTP 403 status code is returned to the client.

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### Block List

Expected result: Access to the above fields in the UA will be blocked.